Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Patent
1998-01-05
2000-05-02
Strecker, Gerard
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
324165, 32420712, 32420725, 340672, 341 6, 702 92, G01D 5244, G01D 308, G01B 2122
Patent
active
060583584
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to absolute angular position encoders, particularly to a device for determining the direction of rotation of said encoders and the plausibility of detected position values.
BACKGROUND INFORMATION
In absolute angular position encoders, actual position values can be transmitted, preferably serially, for example to a controller for further processing, in binary form at predefined time intervals. Since the operation of serial data transmission of all the bits of an actual value of this type that is encoded in binary form takes up a specific time duratio, the real actual value can vary sharply during said operation of the serial data transmission.
A first case of this type is presented when the shaft of the absolute angular position encoder temporarily rotates at a high rotational speed. It may occur, for example, because of an excessive speed that is intrinsically inadmissible. In such case, the factual position of the shaft may change by many distance units between the beginning and end of the serial, bitwise transmission of an actual position value that was detected previously. The subsequent, serially transmitted actual position value then has an absolute magnitude which has changed in an unexpectedly abrupt manner.
A further case of this type is presented when errors occur during the serial data transmission. In this case, high-value bits in the encoding of the actual position value can be falsified in the serial data stream. Such occurrence, for example, may be caused by electromagnetic irradiation. In such case, actual position values may have an absolute magnitude which, induced by the error, changes in an abrupt manner. If such abrupt changes in an actual angular position value are fed to a controller, for example, then both the identification of the rotational direction of the shaft of the angular position encoder, and the testing of the plausibility of the incoming actual position values, are made more difficult.
In normal operation, the direction of rotation of the shaft of the angular position encoder can be ascertained in a simple manner by determining the difference between successive actual values. If the sign of "current actual position value - previous actual position value" is positive, then the rotation is "forward", for example; if a negative sign occurs, then the rotation is "backward". However, a precondition for the functional capability of this method is that the two actual values in the above difference are always positioned so close to each other that such a pair in each case lies either "before" or "after" the so-called "zero point" of the shaft of the angular position encoder. As such, the absolute magnitudes of the two actual values must generally not deviate sharply from each other.
However, the rotational speed of the shaft, and the rapidness of the serial data transmission, must always be matched to each other in such a way that one of the two values of the pair is not acquired "before" and the other value acquired "after" passing over the zero point. In such a case, an erroneous direction of rotation would be determined. For instance, if the old actual value, lying "before" the zero point, is 3550, (corresponding for example to an actual position value of 355.0 degrees), and the new actual value, lying "after" the zero point, is 50 (corresponding for example to an actual position value of 5.0 degrees), then, the difference "current actual position value--previous actual position value", i.e. 50-3550, results in a negative sign. This occurs even though the shaft has been rotated forward over the zero point. On the other hand, actual position values which have been severely corrupted in terms of magnitude as a result of electromagnetic irradiation must also not be used for the difference formation. There is the risk in this case, that an erroneous rotational direction will be determined.
Actual position values which have changed sharply in an unexpected or error-induced manner also constitute a problem if these are checked
REFERENCES:
patent: 4506339 (1985-03-01), Kuhnlein
Siemens Aktiengesellschaft
Strecker Gerard
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